1. Field of the Invention
The present invention relates to an electronic endoscope apparatus which is capable of selecting different image processing conditions in accordance with whether a moving image or a still image is to be displayed.
2. Description of the Related Art
In recent years, solid state imaging devices such as charge-coupled devices (hereinafter referred to as the "CCD(s)") have been widely used as various kinds of imaging means. Television cameras, electronic endoscopes and so forth are known as such imaging means.
In Japanese Patent Laid-open No. 94644/1986, the present assignee proposes an electronic endoscope apparatus which is capable of independently varying the amount of outline emphasis of each color signal by means of an outline emphasis circuit, thereby enabling an improvement in the quality of an image.
FIG. 1 shows the construction of the aforementioned electronic endoscope apparatus.
The illustrated electronic endoscope apparatus according to the prior art comprises an (electronic) endoscope body 10, a video processor 12, an RGB/NTSC monitor 14, an NTSC monitor 16, an RF monitor 18, a recording/reproducing device 20, a light source unit 22 and a laser device 24. A solid state imaging device (for example, a CCD) 30 for imaging a body organ or a body cavity is provided at the distal end of the endoscope body 10. The output of the solid state imaging device 30 is supplied as a two-phase signal to the video processor 12 through an preamplifier 32. Further, a light guide 36 and a laser probe 38 are provided in the endoscope body 10. The laser probe 38 is inserted into, for example, a forceps channel and serves to introduce a laser beam from the laser device 24 into the distal end of the endoscope body 10, irradiating an object with the laser beam. The light guide 36 is constituted by an optical fiber bundle for introducing illuminating light from the light source unit 22 into the distal end, and serves to illuminate the body organ or the body cavity. Since the distal end of the endoscope body 10 is thin, the solid state imaging device 30 consists of a light receiving portion alone and does not have a light shielding-type storing portion which functions as a shutter. A shutter mechanism is provided in the light source unit 22 as will be described later.
An image signal which has been supplied from the preamplifier 32 to the video processor 12 is first input to a CMR amplifier 40. The output signal of the CMR amplifier 40 is passed through a sample and hold circuit 42, a low-pass filter 44, a band correcting circuit 46, an AGC circuit 48, a .gamma. compensation circuit 50, an A/D converter 52 and a selector 54, in that order, and is supplied to a memory circuit 56. The low-pass filter 44 and the band correcting circuit 46 smooth the image signal. The memory circuit 56 is constituted by three frame memories 56-1, 56-2 and 56-3 for storing R, G and B images, respectively. The selector 54 has three output terminals which are connected to the R, G and B frame memories 56-1, 56-2 and 56-3, respectively.
The outputs of the memory circuit 56 are supplied to a 1H memory section 60 through a selector section 58. The 1H memory section 60 is divided into two parts for each color component. Each of the three R, G and B color components are written into the two parts of the corresponding lH memory in an alternately switched manner every horizontal scanning period by the operation of the selector section 58. More specifically, the outputs of the frame memories 56-1, 56-2 and 56-3 are supplied to selectors 58-1, 58-2 and 58-3. Each of the selectors 58-1, 58-2 and 58-3 has two output terminals. The output of the selector 58-1 is connected to a 1H memory 60-1 or 60-2, 2, the output of the selector 58-2 to a lH memory 60-3 or 60-4, and the output of the selector 58-3 to a 1H memory 60-5 or 60-6. The output of the 1H memory 60-1 or 60-2 is connected to a D/A converter 64-1 through a selector 62-1, the output of the lH memory 60-3 or 60-4 to a D/A converter 64-2 through a selector 62-2, and the output of the 1H memory 60-5 or 60-6 to a D/A converter 64-3 through a selector 62-3. The outputs of the D/A converters 64-1, 64-2 and 64-3 are supplied to band correcting circuits 68-1, 68-1 and 68-3 through low-pass filters 66-1, 66-2 and 66-3. The outputs of the band correcting circuits 68-1 and 68-3 are supplied to multipliers 70-1 and 70-3 and multiplied by white balance adjustment signals WB-1 and WB-3 so that the respective white balances are adjusted. The outputs of the multiplier 70-1, the band correcting circuit 68-2 and the multiplier 70-1 are supplied to the R, G and B input terminals of the RGB/NTSC monitor 14, respectively.
Simultaneously, the outputs of the multiplier 70-1, the band correcting circuit 68-2 and the multiplier 70-3 are supplied to an NTSC encoder 74. The output of the NTSC encoder 74 is supplied to both a first input terminal of a selector 76 and the input terminal of the recording/reproducing device 20. The reproduced signal of the recording/reproducing device 20 is supplied to a second input terminal of the selector 76 through a band correcting circuit 80. The NTSC signal output from the selector 76 is supplied through a switch 72 to the NTSC input terminal of the RGB/NTSC monitor 14, directly to the NTSC input terminal of the NTSC monitor 16, and to the RF monitor 18 through an RF modulator 78.
The output of the band correcting circuit 46 is supplied not only to the AGC circuit 48 but also to a voltage divider 85. The voltage divider 85 outputs a reference signal for each R, G and B image during automatic light control. The magnitude of the respective reference signals become small in the order of G, R and B. This is because the magnitudes of the color components of the respective G, R and B image signals become small in that order. Each voltage dividing point of the voltage divider 85 is connected to a corresponding input terminal of the selector 86, and the output signal of the selector 86 is supplied as an automatic light control signal to the light source unit 2 through a low-pass filter 88 and a comparator/amplifier 90.
The video processor 12 further includes an SID driver 91 for generating clock pulses used to drive the solid state imaging device 30. Each circuit in the video processor 14 is timing-controlled by a timing generator 82 or 84. The timing generator 82 receives the signal output from an operating switch 83 provided for controlling irradiation with a laser beam. The outputs of the timing generator 82 are supplied to the sample and hold circuit 42, the selector 54, the memory circuit 56, the selector 86 and the SID driver 91. The outputs of the timing generator 84 are supplied to the frame memory 56, the selector section 58, the 1H memory section 60, the selector section 62 and the NTSC encoder 74. The rate of writing to the memory circuit 56 differs from the rate of reading from the memory circuit 56, and writing to the memory circuit 56 is controlled by the timing generator 82 while reading from the memory circuit 56 is controlled by the timing generator 84. The sections 56 and 86 are controlled in synchronization with each other so that, for example, when either of them selects R, the other also selects R. The selector sections 58 and 62 are controlled so that they select mutually different lH memories.
The light source unit 22 has a lamp 92 for emitting illuminating light to be incident upon the light guide 36. The illuminating light emitted from the lamp 92 is incident upon the light guide 36 through an iris plate 94, an optical system 96 and a rotary filter device 98. The iris plate 94 is constituted by a plate of predetermined thickness and having a plurality of through-holes. The iris plate 94 is rotated by a galvano motor 100 to change an angle with respect to the optical axis of the illuminating light, thereby adjusting the quantity of passing light by using the thickness of the through-holes. The galvano motor 100 is driven by automatic light control signals supplied from the comparator/amplifier 90. As described above, since the magnitude of the automatic light control signals of the respective image signals become smaller in the order of G, R and B, the amount of reduction becomes smaller in the order of G, R and B and, therefore, the levels of the color signals of the respective color components become uniform. The rotary filter device 98 has a shutter function and the function of coloring illuminating light in R, G and B. The rotary filter device 98 is constituted by a disk in which R, G and B color filters are non-continuously arranged around the circumference of a common circle. The non-continuous portions between adjacent color filters serve as a shutter for shielding light to be supplied to the solid state imaging device 30. Holes are formed outside the trailing edges of the respectively color filters in the direction of rotation of the rotary filter device 98, and a start pulse generating through-hole is formed outside the through-hole which is located outside the hole adjacent to the trailing edge of the R filter.
The rotary filter device 98 is rotated by a step motor 102. The step motor 102 rotates at a fixed speed under the control of a servo circuit 104. A light detector 106 is disposed in the vicinity of the edge of the rotary filter device 98. The light detector 106 consists of a light emitting diode and a light sensor, and receives the light passing through the through-hole, generating a read pulse and a start pulse.
The start pulse and read pulse output from the light detector 106 are supplied to the timing generator 82 in the video processor 12 through amplifiers 108 and 110, respectively.
The laser device 24 has a YAG laser 116 interposed between resonant mirrors 118-1 and 118-2, and the YAG laser 116 is excited by an excitation lamp 114 controlled by a lamp controlling circuit & electrical power source 112. The optical path between the YAG laser 116 and the resonant mirror 118-1 is selectively closed and opened by a shutter plate 120 connected to a solenoid 122. Thus, the laser beam of the YAG laser 116 is made incident upon the laser probe 38 in a pulsed manner. On-off action of the solenoid 122 is controlled by the timing generator 82 in the video processor 12.
In the electronic endoscope apparatus having the above-described arrangement, an image of the object which has been imaged by the solid state imaging device 30 is photoelectrically converted into an electrical signal, and the electrical signal is converted into an video signal in the sample and hold circuit 42. The video signal is outline-emphasized by the first band correcting circuit 46. Subsequently, the outline-emphasized signal is passed through the A/D converter 52, converted into synchronized R, G and B signals in the memory circuit section 56 for effecting synchronization of sequential signals. The R, G and B signals are converted into analog video signals in the respective D/A converters 64-1, 64-2 and 64-3 and supplied to corresponding second band correcting circuits 68-1, 68-2 and 68-3, in which the horizontal outline emphasis of the signals are effected.
Accordingly, the outline of the image of a portion to be diagnosed can be emphasized by these first and second band correcting circuits 46 and 68-1, 68-2 and 68-3, whereby the efficiency of diagnosis can be improved.
As will be readily conceived from the construction shown in FIG. 1, a frozen image can be obtained if the same data written in the memory section 56 is repetitively read out when the writing operation of the memory circuit 56 is stopped. In this case, the amount of emphasis of the outline of the frozen image (still image) equals that of emphasis of the outline of a real-time image, that is, a moving image.
In general, however, the resolution and noise of still images differ from those of moving images in terms of visual effects. Accordingly, the above-described example of the prior art still includes factors to be improved.
In such a situation, a reference is as known in which a noise reduction method for use in ultrasonic equipment had been proposed. Such a method, however, contemplates image processing of still images alone. Accordingly, it is impossible to realize real-time processing in terms of processing time and therefore to realize an improvement in the quality of real-time images (moving images) which are normally observed.